Two Vastly Different Election Outcomes That Hinge on a Few Dozen Close Contests

Democrats appear poised to win the House popular vote on Tuesday by a wide margin, with national polls showing sustained disapproval of President Trump — and yet the fate of the chamber is not a foregone conclusion.

On the day before the midterm elections, two vastly different outcomes remain easy to imagine. There could be a Democratic blowout that decisively ends Republicans’ control of the House and even endangers their Senate majority. Or there could be a district-by-district battle for House control that lasts late on election night and perhaps for weeks after.

The first would be interpreted as a repudiation of Donald J. Trump, the second as another example of his political resilience. But the difference turns on just a few percentage points across dozens of House districts that remain exceptionally close, according to New York Times Upshot/Siena College surveys conducted over the last few weeks.

After more than 10,000 interviews, the result, in the aggregate, is that Democrats and Republicans are essentially tied in the 30 districts rated as tossups by the Cook Political Report, with Democrats leading by around half a percentage point.

Democrats need to win only a handful of these tossup districts — perhaps as few as six — to gain the net 23 seats needed to take control, which is why they’re considered favorites. But Democrats haven’t put them away. Instead, those races remain startlingly close. Each of the final 28 poll results in the tossup districts was within the margin of error, and 20 of the 28 were within two percentage points, a margin that pales in comparison with the typical measurement error in a poll.

With so many close contests, even modest late shifts among undecided voters or a slightly unexpected turnout could yield significantly different results, with very different consequences for the government and the future of the Trump presidency.

Over all, the polls comport with the growing consensus among operatives from both parties that Democrats are poised to gain around 35 seats in the House. If the Times/Siena polls were exactly right (they will not be), Democrats would gain 32 seats, assuming the two parties held the seats that were not polled.

All of the conditions remain in place for a so-called wave election, like those that last flipped control of the House in 1994, 2006 and 2010. Democrats hold a commanding lead on the generic congressional ballot (which asks voters whether they intend to vote for Democrats or Republicans for Congress), including an eight-point lead in an ABC/Washington Post poll in Sunday.

But the Republicans have considerable structural advantages in the House that the president’s party didn’t have to the same extent in previous wave elections. They are generally defending districts that voted for the president, a result of partisan gerrymandering and the tendency for Democrats to post lopsided and inefficient victories in urban areas.

The Republican geographic advantage is even more significant in the Senate, where Republicans are all but assured to retain control if they win just three of seven competitive seats where Mr. Trump won by at least nine points in 2016.

The Democrats are poised to defy those structural disadvantages in the House because they’ve put so many Republican-leaning districts into play with a deep and exceptionally well-funded class of candidates.

But Republicans can hope that partisan polarization is just enough to keep even strong Democrats from going over the top. The president has emphasized immigration and other hot-button issues down the final stretch, perhaps in an intentional effort to divide the electorate along the lines of the 2016 election.

If Republicans succeed in polarizing the electorate, they could take advantage of their underlying geographic advantages and hold down their losses in the House and gain seats in the Senate.

Video

Nate Cohn, who covers polling and demographics for The New York Times, describes what informs our election night forecast tool known as the needle.

Alone, a more polarized electorate wouldn’t be enough for Republicans to hold the House. There are too many districts that voted for Hillary Clinton. To retain House control, Republicans would probably need some good luck on top of a more polarized map, or perhaps a broader 2016-like polling error. But a narrow Democratic majority might take weeks to become clear as California and Washington count late mail ballots.

The emphasis on a wide range of possible outcomes isn’t just a matter of hedging by pollsters and analysts after the shock of 2016, when Mr. Trump beat long odds. The uncertainty reflects the sparse data available and the unusually large number of competitive contests. In dozens of key districts, no more than a few polls have been done, making it hard to be confident whether (and where) Democratic or Republican candidates might hold a lead.

Final House polls have historically been less accurate than polls of statewide contests and presidential races. On average, House polls differ from final election results by around eight percentage points. These polls tend to have relatively small sample sizes, increasing the margin of error, and voters tend to be less familiar with House candidates, meaning more “undecideds” until late in the race.

Democrats hope that these common sources of polling error might break their way this time.

Turnout is always uncertain, but it is more variable in lower-turnout elections, like a midterm, when even modest shifts in enthusiasm can transform the electorate. It is a particularly challenging question this year, in part because the turnout in recent midterm elections has been so low and so Republican.

This year’s early vote tallies already make it clear that the turnout will greatly exceed that of four years ago, but it is far less clear how that will translate to actual votes. It is equally unclear whether pollsters have been assuming the high-turnout, more Democratic electorate implied by early voting and the turnout in the special and general elections since Mr. Trump became president.

Over the last few weeks, the share of voters indicating that they’re “almost certain” to vote has increased by 10 points in Times/Siena polls, from 66 percent to 76 percent of the likely electorate.

In a few cases, the turnout in early voting has shown some polls were off in their projection of who will vote. Early voting in several Texas counties has already surpassed the projected electorate of a Times/Siena poll from early October, and the Democratic Senate candidate Beto O’Rourke seems likely to benefit from the higher turnout. A Monmouth poll of California’s 48th District in coastal Orange County showed the Republican incumbent, Dana Rohrabacher, leading by two points with an electorate in which registered Republicans outnumbered Democrats by 18 points. The actual Republican advantage in early voting is down to 12 points and continues to drop as turnout increases.

The final Times/Siena poll of California’s 48th shows the Democrat Harley Rouda leading Mr. Rohrabacher narrowly with an electorate where registered Republicans outnumber Democrats by 10 points, an indicator of the extent that Republicans are struggling in the wealthy suburban bastions of 20th century conservatism.

Democrats can also hope that undecided voters will break their way. It is often supposed that voters will break against incumbents, and Republicans will be in trouble if there’s merit to that assumption. No Republican incumbent has eclipsed 50 percent in any of our polls of the tossup districts.

Undecided voters are also often thought to break toward the party out of power, and perhaps that’s especially likely with stupendously well-funded Democrats spending millions to increase their name recognition in the final stretch. It’s paying off for Democrats in the Times/Siena polls: On average, Democratic challengers are now known by 82 percent of voters in polls over the last 10 days, up from 60 percent in September.

Astonishingly, it’s enough for the Democrats to effectively deny the Republicans the advantage of incumbency that usually helps a party hold the House. In the battleground polls finished over the last 10 days, a larger share of the electorate now has a favorable view of the Democratic challengers than the Republican incumbents, with 48 percent of likely voters holding a favorable view of the Democratic candidate compared with just 46 percent who have a favorable view of the Republican incumbent.

Image

A voter drops off his ballot in Salt Lake City on Wednesday.CreditRick Bowmer/Associated Press

All of this may be adding up to a late shift toward Democrats. The Times reported that both Democratic and Republican operatives see House polls as trending Democratic in the final days, and the last wave of Times/Siena polls are at least consistent with that possibility.

Across the final Times/Siena polls finished over the weekend, Democrats improved their position by an average of three percentage points over the prior poll of the same district. And Democrats have shown surprising late strength in Times/Siena polls of districts that weren’t previously thought to be top-tier contests, like Pennsylvania’s 10th, Florida’s 15th, Georgia’s Sixth and Illinois’s 14th.

At the same time, Republicans have rushed to defend a tier of contests that seem even likelier to remain on their side, like South Carolina’s First, Georgia’s Seventh and Michigan’s Sixth.

If well-funded Democrats are breaking through in this next tier of races, Democrats could easily win more than 45 seats.

But late movement doesn’t necessarily predict the final result. Just ask Mrs. Clinton, who gained slightly in the final polls taken in the weekend ahead of the 2016 election.